This application claims priority to Japanese Patent Application No. P.2000-268964 filed on Sep. 5, 2000 in Japan. The contents of the aforementioned application are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a hydraulic control apparatus for a vehicular automatic transmission for inputting power from an engine.
2. Description of the Related Art
Conventionally, a hydraulic control apparatus of this type is constructed such that a part of oil discharged from a hydraulic pump is supplied to a main hydraulic circuit portion for controlling various types of hydraulic actuators provided on an automatic transmission, whereas a part of the oil discharged from the hydraulic pump is supplied to a lubricating system of the automatic transmission and an oil cooler.
Incidentally, the oil temperature of the automatic transmission tends to be increased when the vehicle is running at high speed. To cope with this, it is desired that the volume of oil that is supplied to the oil cooler is increased to control the increase in oil temperature.
An object of the invention is to provide a hydraulic control apparatus for a vehicular automatic transmission which matches the aforesaid desire.
With a view to attaining the object, according an aspect of the invention, there is provided a hydraulic control apparatus for a vehicular automatic transmission for inputting power from an engine, wherein a part of oil discharged from a hydraulic pump is supplied to a main hydraulic circuit portion for controlling various types of hydraulic actuators provided on the automatic transmission, whereas the part of the oil discharged from the hydraulic pump is supplied to a lubricating system of the automatic transmission and an oil cooler, the hydraulic control apparatus comprising an oil volume changing unit changing a volume of oil to be supplied to the lubricating system and a volume oil to be supplied to the oil cooler, a vehicle speed determining unit determining whether or not the vehicle speed is equal to or faster than a predetermined value, a load determining unit determining whether or not the engine load is equal to or greater than a predetermined value, and a control unit for controlling the oil volume changing unit such that in the event that the vehicle speed is equal to or faster than the predetermined value, whereas the engine load is equal to or smaller than the predetermined value, the volume of oil to be supplied to the oil cooler is increased, whereas the volume of oil to be supplied to the lubricating system is decreased.
When the engine load is low or lower than the predetermined value, the volume of lubricating oil may be small. Thus, with the vehicle speed being equal to or faster than the predetermined value and the engine load being equal to or lower than the predetermined value, the volume of oil to be supplied to the lubricating system can be decreased, whereas the volume of oil to be supplied to the oil cooler can be increased, whereby the increase in oil temperature can be controlled without a shortage of oil being caused. In addition, the decrease in oil volume to be supplied to the lubricating system may reduce the friction loss and suppress the deterioration of oil supplied to the lubrication portions due to agitation of oil.